Thread feed system having an auxilliary conveyor device

ABSTRACT

A thread feed system having a measuring feeder, a supply bobbin supplying thread to the measuring feeder and a textile machine which withdraws the thread from the measuring feeder so as to perform a weaving operation. The measuring feeder includes a storage drum and a winding element which removes the thread from the supply bobbin and winds the thread onto the storage drum. A control device is provided for monitoring the operating conditions of the thread system so as to identify increases in thread tension. The control device is operatively connected to an auxiliary conveyor device having a drivable friction roll which is frictionally engaged with the thread between the supply bobbin and the storage drum. The auxiliary conveyor device is operable so as to provide an increased frictional action on the thread so as to advance the thread at an increased rate to the storage drum so as to preparatorily counteract the thread tension increase and eliminate short picks of the thread in the textile machine.

FIELD OF THE INVENTION

The present invention relates to a method for controlling a thread feedsystem and to a thread feed system having a measuring feeder whichcomprises a storage drum and a winding element for winding thread stockonto the storage drum.

DESCRIPTION OF THE RELATED ART

In a method known from EP-A2-0 195 469, the jet-weaving machine works inaccordance with the weft mixing principle, i.e., identical threads arealternately withdrawn from at least two measuring feeders. A controldevice monitors the operation and reacts to failure, for instance threadbreakage, in such a manner that the one measuring feeder is controlledsuch that it assumes the function of the defective measuring feeder oreven feeders. In a measuring feeder having a plurality of stop elementsdistributed over the circumference of the storage drum, the threadlength is composed of whole turns and of fractions defined by thespacings of the stop elements. In a measuring feeder comprising one-stopelement, the thread length is composed of whole turns and the diameterof the storage drum is adjusted accordingly. Since upon withdrawal ofthe thread along the thread path a thread tension builds up in thethread and since the thread tension is also felt in the turns in thethread stock on the storage drum, the thread length is adjusted suchthat the thread tension building up in the thread stock under normaloperation is taken into account. When a measuring feeder assumes thefunction of a defective measuring feeder, the pick frequency will bedoubled. The speed level rises. The tension within the thread increases.The original adjustment of the thread length is no longer correct; thethread length of the thread section in its relaxed state within thetextile machine will be too short. This will result in short picks.Moreover, when the resistance to withdrawal from the supply bobbinincreases, such a risk will even be enhanced.

In other weaving methods using measuring feeders, the thread length isalso determined and set in advance. Since the supply bobbin is emptiedrelatively rapidly and is capable of carrying a considerable amount ofthread, the diameter of the thread windings on the supply bobbin alsochanges considerably from a new supply bobbin to an empty supply bobbin.With a decreasing diameter of the thread windings the winding-ontension, which is the withdrawal tension of the thread being removedfrom the supply bobbin, increases, as well as the thread tension in thethread stock on the storage drum, so that the set thread length can nolonger be maintained. This entails the risk of short picks. The risk isespecially great at a high speed level.

To avoid short picks, the thread length has so far been set in advanceto the high tension under critical operating conditions, which leads toexpensive waste under normal operating conditions. The thread tensionwhich varies in response to the Operating condition, as well as theundesired effect thereof which varies the set thread length are thustaken into account through a corresponding addition in the threadlength. Measuring feeders can thus not fulfill the task of keeping aconstant thread length in practice, as is actually presupposed intheory.

WO 90/07 600 discloses a thread feed device in which the supply bobbinand the measuring feeder have provided thereinbetween a friction drivewhich performs an assisting conveying function by means of a drivenfriction roll in order to avoid undesired great stresses on the threadand to reduce the number of thread breakages. The surface of thefriction roll is provided with axially defined surface coatings ofdifferent slip tendencies which are arranged side by side and adapted tothe thread qualities of different threads, and of which the respectivelysuited surface coating is used for auxiliary conveyance. The threadfollows a fixed thread path over the friction roll.

It is the object of the present invention to provide a method of theabove-mentioned kind and a thread feed system with the aid of which thepicked thread length can be kept relatively constant and can be setwithout the risk of short picks and with a view to little waste.

SUMMARY OF THE INVENTION

This object is achieved with the method wherein thread is acted upon byan auxiliary frictional force along a thread path from a supply bobbinto a storage drum, and with the thread feed system wherein a mechanicalauxiliary conveyor device is provided between the supply bobbin and themeasuring feeder which supplies a frictional force to the thread. Thefeatures of the thread feed systems which include adjusting thecircumference of the storage drum by a triggerable power accumulator andthe aforementioned auxiliary conveyor device can be combined with oneanother.

Upon occurrence of a critical operating state, an increase in the threadtension in the thread stock which is critical with a view to theobservance of the thread length is counteracted in the method through aconveying frictional action on the thread. The thread turns on thestorage drum are increased in order to increase the thread length to beconsumed despite a thread tension in the turns which is increased undercritical operating conditions, i.e., to such an extent that the threadlength becomes approximately correct after relaxation. The two methodsteps can be used alternatively or additively. In practice, theyguarantee an approach of the function of the measuring feeder to theidealized theoretical function thereof, since the withdrawn threadlength does not vary. The thread length can be adjusted very accuratelyfrom the start so that there is little waste and short picks arenevertheless avoided.

In the thread feed system having the mechanical auxiliary conveyordevice, the auxiliary conveyor device permits a selective action, forinstance during a critical operating state, for avoiding an undesiredincrease in the thread tension in the turns on the storage drum.

In the embodiment wherein the compensating position of acircumferentially-defined longitudinal section can be adjusted, suchadjustment can take place for instance as soon as a critical operatingcondition arises. Since the turns in the stock are then greater, theincrease in tension is approximately compensated by an addition to thethread length. In a storage drum of an invariable diameter and with aplurality of stop elements, the circumferential length of the storagedrum is increased. In a storage drum of a variable diameter and with onestop element the longitudinal section increases the circumferentiallength independently of the respectively set diameter. In both cases thethread feed system has an integrated intelligence which permits anautomatic adaptation of the system to varying operative states.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention shall now be explained with reference tothe drawings in which:

FIG. 1 is a side elevational view diagrammatically showing a thread feedsystem having a measuring feeder and a supply bobbin;

FIG. 2 is a side elevational view showing a thread feed systemcomprising at least two measuring feeders;

FIG. 3a is a side elevational view of an auxiliary conveyor device;

FIG. 3b is a front elevational view of the auxiliary conveyor device ofFIG. 3a;

FIG. 4 is a side elevational view of an alternative embodiment of theauxiliary conveyor device;

FIG. 5a is a front elevational view of a further embodiment of theauxiliary conveyor device in a first working position;

FIG. 5b is a front elevational view of the auxiliary conveyor device ofFIG. 5a illustrated in a second working position;

FIG. 6 is an enlarged side elevational view of a measuring feeder;

FIG. 7 is a side elevational view diagrammatically illustrating afurther embodiment of the measuring feeder;

FIG. 8 is a side elevational view illustrating a further embodiment ofthe auxiliary conveyor device;

FIG. 9 is a side elevational view of the auxiliary conveyor device ofFIG. 8;

FIG. 10 is a side elevational view in partial section of the auxiliaryconveyor device which is diagrammatically illustrated herein;

FIG. 11 is a side elevational view in cross-section illustrating afurther embodiment of the auxiliary conveyor device of FIG. 10.

DETAILED DESCRIPTION

A thread feed system S according to FIG. 1 comprises a supply bobbin P,an auxiliary conveyor device H arranged downstream thereof and ameasuring feeder F which provides a textile machine W, such as a jetweaving machine, with thread sections of a set thread length. Thread Ywhich is withdrawn from thread windings 1 on supply bobbin P passesthrough the auxiliary conveyor device H which is optionally secured (asoutlined in broken line) to the inlet end of the measuring feeder F, ismoved in the measuring feeder F on a storage drum 7 in a plurality ofturns into a thread stock 8 and is withdrawn clockwise and overend thestorage drum 7.

The supply bobbin P can have assigned thereto a sensing device 2 forsensing the diameter of the thread windings 1 to produce a signal assoon as diameter d1 of thread windings 1 falls below a diameter d2.Alternatively, the sensing device 2 could also monitor the amount ofunwound thread and produce a signal from a predetermined residual amountof thread onwards.

The measuring feeder F has a housing 3 in which a control means 4 isaccommodated for a drive motor 5 of a winding element 6 and in which thestorage drum 7 is non-rotatably supported. The storage drum 7 hasassigned thereto a stop device 11 which has arranged therein at leastone retractable and extendable stop element 12. With only one stopelement 12, it is possible to adjust the diameter of the storage drum 7for setting the thread length. In cases where a plurality ofcircumferentially distributed stop elements 12 are provided in the stopdevice 11, the storage drum 7 has an invariable diameter.

A respective section is introduced into a compartment 14 with a pickingdevice 13 of the textile machine W. A central control device 15 isconnected to the measuring feeder F, optionally to the auxiliaryconveyor device H or drives 16 thereof, or optionally to the sensingdevice 2. A thread tension or thread speed meter 30 may be provided onthe thread path and connected to control device 15. Further thread feedsystems of a similar type can be linked with control device 15. On thestorage drum 7, a circumferentially defined longitudinal section 9(outlined in broken line) can be moved by means of a power accumulator10, which is symbolized by an arrow, from a passive position withdrawninto or below the enveloping surface of the storage drum 7, into thecompensating position shown in broken line for increasing the turns onstorage drum 7.

A thread stock 8 is formed on storage drum 7 during operation. Thethread length per pick is set either with the aid of the storage drumdiameter or by selecting the stop elements 12 to be respectivelyactuated, i.e., in consideration of the thread tension created duringwinding in thread stock 8. Thread Y is elastic in longitudinaldirection, so that the thread tension in the turns has the effect thatduring relaxation the picked thread section will shorten to the threadlength needed in the compartment. As soon as weaving machine W is readyto withdraw a section, the stop element is disengaged. Shortly beforethe time when the set thread length is removed, the stop element 12 or apredetermined stop element 12 will be engaged, so that thread Y will bestopped when the thread length has been reached. Drive 5 supplementsthread stock 8 on the storage drum 7 subsequently and/or in themeantime. When the diameter of thread windings 1 on supply bobbin Pfalls below d2, the withdrawal resistance has risen considerably. Thisconstitutes an operating condition which is critical with respect to theobservance of the set thread length, since at an increased threadtension in the turns on the storage drum 7 the withdrawn thread sectionwill shorten to a higher degree after picking and fall below the setthread length. When such a critical operating condition arises, thecontrol device 15 receives, for instance from sensing device 2, a signalon the basis of which drive 16 of the auxiliary conveyor device isactivated or the auxiliary conveyor device H is moved into frictionalengagement with thread Y. As a result, the thread tension in the threadpath to the measuring feeder 7 and in the turns on storage drum 7 isreduced to a lower level to maintain the thread length introduced intocompartment 14. Alternatively or additively, the power accumulator 10 istriggered and the longitudinal section 9 is brought into itscompensating position, whereby the thread turns 8 are increased, inparticular the thread turns 8 which have been wound up after theadjustment of the longitudinal section 8. A thread section is thenreleased that is per se longer and has again the set thread length inits relaxed form.

The auxiliary conveyor device H operates or advances the yarn with aslip, optionally such that it intensifies its influence as an auxiliaryconveyor means approximately linearly or analogously with the decreasein diameter of thread windings 1. More particularly, the auxiliaryconveyor device pushes or advances the yarn, although some slippage ofthe yarn occurs relative to the auxiliary conveyor device. Furthermore,it is possible to move the longitudinal section 9 with a delay withrespect to the activation of the auxiliary conveyor device H into thecompensating position. The auxiliary conveyor device H and/or thelongitudinal section 9 can also be operated in response to the signalfrom the measuring device 30 or a thread breakage detector in anothermeasuring feeder F.

After the end of the critical operating condition, for instance after achange to a new supply bobbin P or after the elimination of a threadbreakage, the auxiliary conveyor device H is stopped or brought out ofengagement and/or the longitudinal section 9 is moved back into thepassive position.

In FIG. 2, the thread feed system comprises two (or a plurality of)measuring feeders F1, F2 with upstream auxiliary conveyor devices H1, H2and supply bobbins P and a central control device 15'. The two threadsare identical. The measuring feeders F1, F2 operate in accordance withthe weft mixing method, i.e., alternately, wherein the change can beinitiated by the picking device 13' or the central control device 15'. Achange is possible after every pick or only after a plurality of picks.The purpose of the weft mixing method is to improve the quality of thewoven fabric and to reduce the speed level in every measuring feeder.

In case of a fault message from one of the measuring feeders F1, F2 (forinstance in case of thread breakage) the control device 15' puts thefaulty measuring feeder temporarily out of operation and prompts atleast one of the other measuring feeders to take over the function ofthe faulty measuring feeder. This yields a higher picking frequency at ahigher speed level for this measuring feeder and an operating conditionwhich is critical with respect to the observance of the set threadlength. That is why the control device 15' actuates either therespective auxiliary conveyor device H1, H2 and/or the longitudinalsection 9 for adjustment into the compensating position. In eachmeasuring feeder F1 and F2, respectively, it is either only theauxiliary conveyor device H1, H2 or only the adjustable longitudinalsection 9 that may be provided for. However, it is also possible, asshown, to provide and use both components in combination. Furthermore,it is possible, as in FIG. 1, to sense either the diameter of the threadwindings on the supply bobbin P and/or the thread tension or threadspeed and to use the signals obtained for control purposes.

In FIGS. 3a and 3b, the auxiliary conveyor device H, H1, H2 comprises anelectric motor M as a drive 16 for a friction roll 18 arranged on amotor shaft 17, which is wrapped by thread Y with an angled. Frictionroll 18 operates with a slip whereby the yarn slips relative to thefriction roll. The friction roll 18 must therefore be provided in thecontact area with at least one circumferential speed that is higher thanthe instantaneous withdrawal speed of yarn Y from the supply bobbin, forinstance by 10-15%. This withdrawal speed from the supply bobbin is alsoreferred to as the winding-on speed of the yarn Y onto the storage drum7. The intensity of the auxiliary delivery can be modified by changingthe wrap angled, for instance by adjusting the auxiliary conveyor deviceH, H1, H2 in the direction of a double-headed arrow 19. This adjustmentcan also be used for activating the auxiliary conveyor device at all.

As shown in FIG. 4, drive 16' of the auxiliary conveyor device H, H1, H2is a compressed-air turbine 21 which is mounted in a housing 20 andacted upon via an inlet 22 and which prompts the used compressed-air toflow out via an outlet 23. Friction roll 18 is mounted on turbine shaft17 for rotation therewith.

In FIGS. 5a and 5b, the auxiliary conveyor device H is composed of twofriction drives H' and H", with friction drive H' auxiliarily conveying,for instance, permanently, thread Y by means of friction roll 18 whilethe second friction drive H2 is activated by means of an adjusting unit25 in a guide 24, if necessary. According to FIG. 5b, the friction roll18 of the second friction drive H" becomes only operative under anoperating condition which is for instance critical for the observance ofthe thread length, so that the thread Y is deflected on both frictionrolls. The deflection angles on both friction rolls 18 can be changed bycorrespondingly adjusting the second friction drive H2, so that theauxiliary conveying effect on the whole can be both friction rolls 18permanently rest on thread Y and where only one is driven to compensatefor the braking of the other one may be expedient. It is only in of caseof need that both rolls are driven.

In the measuring feeder F, F1, F2 according to FIG. 6, the storage drum7 is formed as a rod cage with axial rods 26. In case the stop device 11includes a plurality of stop elements 12, the diameter of the storagedrum 7 is invariable. If, as outlined, there is only provided oneelement 12, it is possible to adjust the outer diameter of the storagedrum 7, for which purpose rods 26 mounted on spokes 33 which areadjustable individually or jointly radially in the direction of adouble-headed arrow 34. Irrespective of whether the storage drumdiameter is fixed or variable, at least one rod 26 or a longitudinalsection 9 arranged at a rod 26 is adjustable between the passiveposition shown in broken line, in which it is approximately in alignmentwith the enveloping surface of storage drum 7, and the compensatingposition shown in full lines. The longitudinal section 9 can be adjustedoutwardly in parallel with itself or with the axis of the storage drumor can be pivoted outwardly about a tangential pivot axis located nearthe front end of the storage drum. The power accumulator 10 is seatedinside the storage drum 7. The longitudinal section 9 or the rod orfinger, respectively, is optionally retained in the passive positionwith the aid of a lock 27. A trigger 28 outside storage drum 7 isoperated for releasing lock 27, thereby enabling power accumulator 10 toadjust the longitudinal section. After the end of the critical operatingcondition the longitudinal section 9 is moved back into the passiveposition by means Of a resetting drive 28 and is locked. The adjustablerod 26 or the longitudinal section 9 should extend on the one hand underthe outlet of winding device 6 and on the other hand at least over thelength of thread stock 8 to act on all turns.

The thread feed system S according to FIG. 7 is arranged on a weavingmachine, such as an air-jet weaving machine W, which includes a threadselection means A which is connected to a control device C via a line57. A plurality of measuring feeders F, F1, F2, for instance four, arearranged upstream of the selection means A, with an auxiliary conveyordevice H being respectively provided upstream thereof. Every thread Yruns with a deflection via a rotational friction surface 43 of theauxiliary conveyor device H into the measuring feeder F, F1, F2, andfrom there to selection means A.

The auxiliary conveyor device H has a drive 42 for the rotationalfriction surface 43, the drive being an electromotive, pneumatic ormechanical drive. However, it is also possible that drive 42 is coupleddirectly or via a gear to the drive of the measuring feeder. Therotational friction surface 43 has a plurality of adjacentcircumferential portions, for instance three circumferential portions44, 45, 46 with different friction coefficients. The rotational axis ofthe rotational friction surface 43 is designated by X. Thread guidingelements 47, 48 are mounted on a support 49 which can be moved, forinstance, pivoted, in a bearing 50 between several positions. An arm 51which is connected to support 49 projects into the operating range of aplunger 53 of a drive 52 of an adjusting mechanism E. A spring holds arm51 either on stops (not shown) or on plunger 53. Drive 52 is connectedvia a transmission connection 55 to the control device C and can becontrolled by signals. A thread breakage or thread running detector Dcan be arranged in the thread path of each thread Y, the detector beinglinked via a line 56 to control device C.

During normal operation the control device C influences the selectionmeans A such that threads Y can be removed alternately. All of theauxiliary conveyor devices H can be driven. Threads Y are, for instance,deflected on the circumferential portions with the smallest frictioncoefficients (these may be smooth or polished). In case of threadbreakage or a critical operating condition with an increased winding-ontension level, this will be reported to the control device C, in case ofthread breakage, for instance, via detector D. The control devicecontrols the selection means A such that the broken thread, or thepresently faulty measuring feeder, is ignored and excluded from thesupply of the remaining threads to the textile machine which are thensupplied at an increased rate to compensate for the unused measuringfeeder. The winding-on speed level will therefore rise in the properlyfunctioning measuring feeders. It is possible to allocate theintermediate storage function for the defective measuring feeler to onemeasuring feeder only. The winding-on speed level will then increase inthis measuring feeder F only. At the same time, the control device Cwill supply a signal to drive 52 to shift the thread to acircumferential portion 44, 45, 46 having a higher friction coefficientand to increase the delivery rate. When several measuring feeders sharethe intermediate storage function of the defective measuring feeder,drives 52 of all of the auxiliary conveyor devices B are activated.

It is expedient when the rotational frictional surface 43 comprises aplurality of circumferential portions with different frictioncoefficients to be able to increase or vary the delivery rate severaltimes. The rotational speed of the rotational friction surface 43 is sohigh from the start that a speed surplus exists at any rate. However, itis also possible to increase the rotational speed in steps or in acontinuously variable manner in accordance with the increase in thewinding-on speed level.

After the elimination of the thread breakage or thread breakages, thecontrol device C can again control the selection means A in the originalmanner, so that all of the measuring feeders F can be used. At the sametime, signals are transmitted to drives 52 for shifting threads Y tocircumferential portions 44, 45, or 46 which have low frictioncoefficients for reducing the delivery rate.

In FIG. 7, and also in FIG. 10, thread Y is adjusted relative to therotational friction surface 43 which is immovable in the direction ofthe rotational axis X.

According to FIG. 8 the rotational frictional surface 43 is adjusted inthe direction of the rotational axis X relative to thread Y extending inan unchanged position or with an unchanged geometry.

A housing 58 contains a compressed-air turbine 59 as a drive whosewithdrawal shaft 60 drives a friction roll 62. The thread guidingelements 61 are stationary. The adjusting mechanism E acts on frictionroll 62 in the direction of a double-headed arrow 63 so as to adjust theroll in the direction of rotational axis X.

In FIG. 9, thread Y is held with an unchanged geometry when the housing58 of the auxiliary conveyor device H with friction roll 62 is adjustedin the direction of rotational axis X by the adjusting mechanism E (inthe direction of a double-headed arrow 65). To this end, housing 58 ismovably held in guides 64. Outlined stops secure the end positions ofthe housing 58. Friction roll 62 is secured to the output shaft 60 inthe direction of the rotational axis X in an immovable manner and forrotation therewith. The rotational friction surface 43 has providedtherein at least two adjacent circumferential portions 44, 45 withdifferent coefficients of friction.

The thread guiding elements 47, 48 are, for instance, thread eyes orforks on a support 49 mounted on a plunger 70 of drive 52 (switchingmagnet or pneumatic or electromotive drive member). In thisconfiguration according to FIG. 10, drive 52 is fixed with a mounting 69onto housing 58. A stationary thread eye 61 and a compressed-airconnection 67 (for supply of turbine 59), as well as anelectromagnetically operable valve 68 for switching on and off and forregulating the amount of compressed air so as to set the turbine speedare positioned between thread stock 1 (not shown) and the rotationalfrictional surface 43. The auxiliary conveyor device H is secured with aholding flange 71 to an abutment, for instance on the measuring feederor the bobbin frame of bobbins P. An arc-shaped slot 72 makes itpossible to pivot housing 58 for setting an optimum thread geometry. Thethread guiding elements 47, 48 are offset by about 90° relative to eachother about the rotational axis X. It is also possible to vary theoffset and to influence the delivery rate through the wrap angle.

The rotational frictional surface could be conical or comprise conicalcircumferential portions 44, 45, 46. Alternatively, the circumferentialportions 44, 45, 46 could comprise different diameters and could beseparated by, for instance, rounded transitions which can easily beswept over by thread Y. The circumferential portions 44, 45, 46 consist,for instance, of a ceramic material, of metal or of heat-treated ortreated metal or of a plastic material with a high resistance toabrasion, a uniform surface roughness and a constant frictioncoefficient.

In a longitudinal section, FIG. 11 illustrates a possible embodiment ofvalve 68 of FIG. 10. Valve 68 is here a valve which can beelectromagnetically switched over between a shut-off position and apassage position and includes a housing 73 which has mounted thereon aswitching magnet 74 with a coil 75 and an axially movable armature 76.Armature 76 is equipped at its bottom end with a small sealing plate 77and projects into a chamber 78 of housing 73 which the compressed-airconnection 67 leads to. Armature 76 is expediently pressure-compensated,so that it can easily be adjusted despite the pressure prevailing inchamber 78. Armature 76 is expediently held by a spring (not shown) inthe illustrated shut-off position in which it presses the small sealingplate 77 onto a valve seat 89. Upon excitation of coil 75 it is drawntowards a rear stop, thereby releasing the connection from chamber 78 toan axial channel 79 of a flow path to a turbine connection 86. Abranched hole 88 is branched off from axial channel 79 and is optionallyconnected to an adjusting drive, for instance, for a pivotal adjustmentof the auxiliary conveyor device H. When not needed, the branchedchannel 88 is closed by a stopper (as shown).

The axial channel 79 terminates in a hole 80 of a small diameter Whichextends at the side facing away from the axial channel 79 through acoaxial hole of a large diameter. A differential piston 82 is slidablyguided in holes 80 and 81 between a control position shown in full linesand a release position spaced apart from axial channel 79. Thedifferential piston 82 has an end section 83 of a small diameter whichengages into hole 80 and contains a restricting path 84. Radial controlpassages 85 which are in flow communication with the axial channel 79lead to an axially defined turned groove 87 of the end section 83.

In the illustrated shut-off position of valve 68 and with thedifferential piston 82 being in the control position, the axial channel79 is connected to the turbine connection 86 via control passages 85which set a specific amount of air with their cross-sections. The frontside of the end section 83 separates the turbine connection 86 from theaxial channel 79.

When valve 68 is switched over into the passage position, the armature76 is drawn into is end position at the right side upon excitation ofcoil 75. The small valve plate 77 lifts from valve seat 89. Chamber 78is connected to the axial passage 79. Compressed air acts on thedifferential piston 82 on the front end surface of end section 83 anddisplaces it into the release position to the left. The annular endsurface of the large-diameter member of the differential piston 82 isexpediently pressure-relieved. The axial channel 79 is directlyconnected to the turbine connection 86, thereby permitting acompressed-air throughput to the turbine which is substantiallyuncontrolled. The restricting path is dimensioned such that the pressureprevailing in the axial channel 79 propagates towards the largeractuation side of the differential piston 82 as soon as thecompressed-air turbine has been accelerated to a sufficient speed. Owingto the difference in area between holes 81 and 80, the differentialpiston is again pushed back into the illustrated control position inwhich it separates the axial channel 79 from the turbine connection 86.The compressed air is forced through the control passages 85 whosecross-section is designed for a predetermined amount of aircorresponding to a specific speed of the turbine.

Valve 68 could also be operated mechanically or pneumatically uponactivation of the compressed-air supply.

In view of the foregoing, in the embodiment wherein the auxiliaryconveyor device has at least one friction drive which includes adrivable friction roll Upon which the thread rests, the thread isconveyed by an auxiliary means on the friction roll in the criticaloperating state and is so to speak pushed after to avoid an undesiredincrease in tension in the thread stock.

An expedient embodiment follows wherein the friction roll is disposed ona shaft which shaft is connected to a compressed-air turbine or anelectric motor. A compressed-air turbine can be produced in aninexpensive manner, it can be of a small structure and controlledeasily. The drive medium of compressed air is most of the time availableat the textile machine at any rate.

The embodiment may also include two or more individually drivablefriction rolls and/or an adjusting device provided for changing the wrapangle of the friction rolls. Additionally, this arrangement permits amodification of the auxiliary delivery of the thread, i.e., theauxiliary delivery is adapted to the respective operating condition andto the tension conditions in the thread, respectively.

Whenever the demands made on the auxiliary delivery of the thread changeduring operation, for instance upon occurrence of a critical operatingcondition, the delivery rate will be adapted accordingly by conveyingthe thread on a circumferential portion of the rotational frictionsurfaces in an auxiliary manner, with the circumferential portion havinga friction coefficient differing from that of the previously usedcircumferential portion. The delivery rate can thus be increased orreduced and adapted to the changed needs in this manner. The rotationalfriction surface is always driven with a speed surplus with respect tothe winding-on speed of the thread onto the storage drum so as to conveythe thread with a slip.

In the embodiment wherein the drive of the adjusting mechanism isconnected to a control device that varies the winding-on speed of themeasuring feeder, the winding-on speed level is varied in such a mannerthat the thread is movable from one circumferential portion to anotherone on the auxiliary conveyor device during a predetermined increase inwithdrawal speed level so as to also increase the delivery rate of thethread. The circumferential portion of the rotational friction surfacewith the different friction coefficient is used for auxiliary conveyingpurposes whenever an increase in the winding-on speed level does effectan undesired increase in the winding-on tension level in the thread andin the thread stock.

In the embodiment wherein the adjusting mechanism comprises at least onethread guiding element that is adapted to be brought into engagementwith the thread in the direction of the rotational axis, the threadguiding element can be adjusted in this direction of the rotational axisbetween a plurality of positions corresponding in number and arrangementto the circumferential portions of the rotational friction surfaceeither in one step or in a continuously variable manner. The threadthereby is adjusted in the direction of the rotational axis relative tothe rotational friction surface and shifted from one circumferentialportion to another one.

The embodiment wherein the two thread guiding elements are offset byabout 90 degrees and assigned to the rotational friction surface is of asimple construction and functions in a reliable manner. The two threadguiding elements are arranged on a support that is mounted on a plungerwhich plunger is adjustable and parallel with the rotational axis byhaving a magnetic, pneumatic or electromotive drive. The drive shiftsthe support and the thread guiding elements so that the thread isdisplaced from one circumferential portion to another one. It remainssubstantially deflected at about 90 degrees. However, it is alsopossible to change the offset of the guiding elements to vary the threaddelivery rate via the wrap angle.

The embodiment wherein the drive is mounted on a housing which housingaccommodates either the compressed-air turbine or, optionally, apressure accumulator, the friction roll is mounted on an output shaftprojecting from the housing. In particular, this embodiment uses thecompressed-air turbine to reach the necessary speed level of therotational friction surface. The turbine can easily be controlled.However, an electric motor as a drive source can also be expedient.

The embodiment wherein the compressed-air connection and the turbineconnection have an electromagnetic valve therebetween which isswitchable between a shut-off position and a pass-through position, isespecially expedient because the valve is not only responsible for theactivation or deactivation of the compressed-air turbine, but includes,with the differential piston, an element which performs a controlfunction in response to pressure and independently releases the flowpath in a substantially unrestricted manner for the rapid start of thecompressed-air turbine. The valve assumes its control positionindependently as soon as the compressed-air turbine has been acceleratedto a sufficient speed and then adjusts the amount of air for the turbineto keep the necessary operating speed. Hence, the differential pistonconstitutes a starting aid for the compressed-air turbine and thencontrols the amount of air to avoid any waste of compressed air. Whenthe differential piston is used, a pressure accumulator can optionallybe dispensed with.

The alternative embodiment wherein the rotational friction surface isarranged on a drivable friction roll has the advantage that the threadin the thread path need not be adjusted because either the friction rollor the auxiliary conveyor device is adjusted axially to move or shift adifferent circumferential portion to a position below the thread. As arule, the auxiliary conveyor device provides for an increased weftfrequency and thus for an improved exploitation of the capacity of theweaving machine without any increase in the thread breakage percentage.

In the embodiment wherein the circumferential portions have acylindrical shape and are provided with different diameters and haverounded or bevelled transitions therebetween, the different diametersare responsible for higher or lower delivery rates.

In the embodiment wherein the rotational friction surface or thecircumferential portions have a conical shape, the delivery rate iscontinuously variable. In both cases, the drive of the auxiliaryconveyor device can optionally run at about the same speed even in thecase of a changing withdrawal speed level.

In the embodiment wherein the longitudinal section of the storage drumis an axial rod formed as a rod cage, the rod or a rod inside the rod ofthe rod drum is abruptly moved into the compensating position wheneverthe critical operating condition arises. The circumferential length ofthe storage drum thereby is increased. An addition to the set threadlength compensates for the increasing thread tension. The relaxed threadsection which is extended by the addition will then predominantly complywith the set thread length. The resetting drive will later reset the rodinto the optionally locked passive position.

In the embodiment wherein further measuring feeders are provided whichare connected to a control device, the auxiliary conveyor device or theadjusting mechanism and/or the trigger of the power accumulator isactivated by the control device when the same initiates the criticaloperating condition. In the weft mixing method this is the case wheneverone of a plurality of measuring feeders temporarily takes over thefunction of at least one other measuring feeder.

In the embodiment wherein the recognition means includes athread-tension, thread-speed, or drive-speed measuring device or athread breakage detector or thread monitor, an actuation is performedwhenever the sensing device detects that the winding-on tension willexcessively rise on account of the diameter of the supply bobbin and/orthe remaining thread amount on the supply bobbin.

In the embodiment wherein a recognition means is provided forrecognizing operating conditions or changes in operating conditions, therecognition means activates the auxiliary conveyor device and/or thepower accumulator upon occurrence of a critical operating condition.

In the embodiment wherein the recognition means includes athread-tension, thread-speed, or drive-speed measuring device or athread breakage detector or thread monitor, the recognition means hasprovided therein measuring devices or sensors which directly sense thethread and produce signals representative of the operating conditions ora change in the operating conditions. The thread tension can, forinstance, be sensed with a tensiometer which produces a signal at aspecific tension limit. The speed measuring device for measuring thewinding-on speed of the thread can be set to a specific speed limit. Thethread breakage detector (thread monitor) signals during weft mixingweaving that the measuring feeder in question has to take over thefunction of another one and that the thread tension will rise.

It is important to note that the method and the thread feed system willrespond to a change towards a critical operating condition sufficientlyrapidly. The termination or changing of the auxiliary conveyance and/orthe reduction of the turns in the thread stock after the end of thecritical operating condition can be performed at a relatively slow pacebecause excessively long free ends of the weft threads which occurduring a short period can be tolerated.

Also, in the thread-processing thread feed system wherein a plurality ofmeasuring feeders are provided, a respective auxiliary conveyor deviceprovided upstream of each measuring feeder includes a drivable adjustingmechanism to vary the frequency or delivery rate of the thread beingprovided to the storage drum. The thread consumed at a higher frequencyis conveyed in an auxiliary manner after thread breakage to acircumferential portion which has a higher coefficient of friction. Thedelivery rate is thereby increased and an undesired increase in thethread winding-on tension and the tension level in the turns on thestorage drum is compensated. The pick length does not changesignificantly, so that the pick length can be set to be optimally shortin advance. The result is a minimized loss of thread material withoutthe risk of excessively short thread lengths.

We claim:
 1. A method for controlling a thread feed system comprising atleast one measuring feeder which includes a storage drum for storingturns of thread thereon, a supply bobbin associated therewith forsupplying said thread to said storage drum, a winding element forwinding said thread in said turns on said storage drum and a textilemachine which withdraws said thread from said measuring feeder forintroduction into a weaving compartment of said textile machine, saidthread being withdrawn from said measuring feeder in thread sections ofa thread length which is set on said measuring feeder, said methodcomprising the steps of supplying thread along a thread path from saidsupply bobbin to said storage drum, winding said thread on said storagedrum, and withdrawing said thread from said storage drum to said textilemachine, the method being adapted to be performed at least temporarilyunder operating conditions in which a thread tension in said turns ofthread on said storage drum increases with an increasing winding speedand/or an increasing resistance to withdrawal from said supply bobbin,the improvement comprising counteracting an increase in the threadtension in said thread turns on said storage drum in response to saidoperating conditions by applying an additional frictional conveyingaction on said thread in said thread path between said supply bobbin andsaid storage drum so as to convey said thread at an increased deliveryrate, and sensing said operating conditions which increase said threadtension, said additional frictional action being applied to said threadin response to said sensing of said operating conditions.
 2. A threadfeed system comprising at least one measuring feeder, a supply bobbinassigned thereto for supplying a thread to said measuring feeder and atextile machine which withdraws said thread from said measuring feederin thread sections of a thread length which is set on said measuringfeeder, said measuring feeder including a storage drum for storing turnsof said thread in a thread stock on said storage drum and a windingelement which is rotatable relative to said storage drum by drive meansfor rotating said winding element to form said turns of said threadstock at a winding-on speed, the improvement comprising a control devicewhich is provided for sensing and/or monitoring and/or recognizingoperating conditions which increase a thread tension in said threadturns on said storage drum, and an auxiliary conveyor device which hasat least one friction drive with a drivable friction roll and isdisposed in a thread path between said supply bobbin and said measuringfeeder, said auxiliary conveyor device being connected to communicationmeans for communicating said auxiliary conveyor device with said controldevice, said auxiliary conveyor device being adapted to be activated bysaid control device for providing an additional frictional delivery ofsaid thread to said measuring feeder in response to said operatingconditions to counteract an increase in said thread tension.
 3. Thethread feed system according to claim 2, wherein during operation ofsaid thread feed system a longitudinal section which is defined in acircumferential direction of said storage drum can be adjusted from apassive position into a compensating position projecting outwardly of anadjacent circumferential surface of said storage drum, a triggerablepower accumulator for abruptly displacing said longitudinal section intosaid compensating position being provided in said storage drum.
 4. Thethread feed system according to claim 3, wherein said control deviceincludes a sensing device for sensing the diameter or amount of threadon said supply bobbin said sensing device being in communication withsaid auxiliary conveyor device and the adjusting mechanism thereofand/or said power accumulator and said trigger thereof through saidcommunication means, said auxiliary conveyor device and said adjustingmechanism and/or said power accumulator being activated by said controldevice as said thread is supplied from said supply bobbin from apredetermined bobbin diameter or a predetermined amount of threadonwards.
 5. The thread feed system according to claim 3, wherein saidlongitudinal section is an axial rod of said storage drum which isformed as a rod cage, said rod being connected to said storage drum soas to be adjustable in parallel with itself or be pivotable about anaxis positioned near a front drum end at a withdrawal side thereof, saidpower accumulator being arranged inside said storage drum at saidlongitudinal section, a mechanical or contactless trigger for said poweraccumulator or for a lock being provided radially outside of saidstorage drum for triggering said power accumulator to said compensatingposition, a mechanical resetting drive for said longitudinal sectionbeing provided radially outside said storage drum for resetting saidpower accumulator to said passive position.
 6. The thread feed systemaccording to claim 3, wherein at least one further measuring feeder isprovided on said textile machine, said measuring feeders being connectedjointly to said control device for an alternate operation at lowfrequencies or for the individual operation of only one measuring feederat a correspondingly higher frequency upon a failure or malfunction ofsaid other measuring feeder in response of a thread breakage detector,said control device being in control communication with said auxiliaryconveyor device and/or said trigger of said power accumulator by saidcommunication means in such a manner that during individual operation ofsaid one measuring feeder the auxiliary conveyor device thereof isactivated and/or the power accumulator thereof is triggered.
 7. Thethread feed system according to claim 3, wherein said control devicecomprises an electronic recognition means for recognizing the operatingconditions of said thread feed system, said recognition means being incommunication via said control device with said auxiliary conveyordevice and the adjusting mechanism thereof and/or said power accumulatorand said trigger, respectively.
 8. The thread feed system according toclaim 7, wherein said recognition means includes a thread-tension,thread-speed or drive-speed measuring device or a thread breakagedetector or thread monitor.
 9. The thread feed system according to claim2, wherein said friction roll is arranged on a shaft which is connectedto a compressed-air turbine, flow path means being connected to saidturbine between a turbine connection and a compressed-air connection fordefining a flow path therebetween.
 10. The thread feed system accordingto claim 9, wherein on a housing of said auxiliary conveyor devicebetween said compressed-air connection and said turbine connection thereis provided a valve which is operable between a shut-off position and apassage position for adjusting said flow path, said valve in the flowpath between said turbine and compressed-air connections including adifferential piston which can be acted upon at one end directly and atthe other end via a restricting path, said differential piston beingmovably guided in response to pressure between a release position and acontrol position, said differential piston comprising control passageswhich in the control position adjust the amount of air flowing throughsaid flow path for said turbine, and in the release position release theflow path in a substantially unrestricted manner.
 11. The thread feedsystem according to claim 2, wherein two or more individually drivablefriction rolls and an adjusting device are provided for changing a wrapangle of said thread on said friction rolls.
 12. The thread feed systemaccording to claim 2, wherein a rotational friction surface of saidfriction roll comprises a plurality of circumferentially closedcircumferential portions with different friction coefficients which aredisposed side by side, a drivable adjusting mechanism being providedwhich includes drive means for shifting said thread from one saidcircumferential portion to another one of said circumferential portionsduring said winding of said thread by shifting said circumferentialportions relative to said thread in the direction of a rotational axisof said rotational friction surface so as to vary the thread deliveryrate of said thread.
 13. The thread feed system according to claim 12,wherein said circumferential portions have a cylindrical shape and areprovided with different diameters, optionally with rounded or bevelledtransitions from one diameter to the next one.
 14. The thread feedsystem according to claim 12, wherein a plurality of measuring feederswhich temporarily store identical threads are adapted to be provided onsaid textile machine;a respective said auxiliary conveyor device beingprovided upstream of each of said measuring feeders and including a saidfriction roll which has a said drivable adjusting mechanism for relativeshifting of said thread from a said circumferential portion to anothersaid circumferential portion by shifting said circumferential portionsrelative to said thread in the direction of said rotational axis so asto vary the delivery rate of said thread, said control device beingconnected to a thread selection means of said weaving machine foralternately using said threads which are temporarily stored on saidmeasuring feeders, said control device activating said selection meansupon a breakage of said thread on at least one of said measuring feedersto ignore said broken thread and to transfer a temporary thread storingfunction to one or all of said other measuring feeders, transferconnections being arranged between said control device and the drivemeans of said adjusting mechanisms for communicating drive signals ofsaid control device to said drive means for increasing, upon said threadbreakage, the delivery rate of said thread or said threads for saidother thread measuring feeders to which said temporary thread storingfunction has been transferred.
 15. The thread feed system according toclaim 12, wherein said rotational friction surface is arranged on saidfriction roll which is driven by drive means for driving said frictionroll, said auxiliary conveyor device including support means foradjustably supporting said friction roll so that said rotationalfriction surface is movable in the direction of said rotational axis,and said adjusting mechanism being adapted to shift said friction rollor said auxiliary conveyor device in said direction of said rotationalaxis to adjust said friction roll relative to said thread.
 16. Thethread feed system according to claim 12, wherein said drive means ofsaid adjusting mechanism is connected to said control device, saidcontrol device including thread selection means of said textile machinewhich varies the winding-on speed level of said thread being withdrawnfrom said measuring feeder in such a manner that at a predeterminedincrease in the winding-on speed level, said thread is movable by saidadjusting mechanism for moving said thread from one circumferentialportion to another one in said auxiliary conveyor device to increase thedelivery rate of said thread.
 17. The thread feed system according toclaim 16, wherein said adjusting mechanism comprises at least one threadguiding element connected to said drive means which is at least adaptedto be brought into engagement with said thread in the direction of saidrotational axis in at least one step or in a continuously variablemanner, said thread guiding element being adjusted in the direction ofsaid rotational axis by said drive means between a plurality ofadjustment positions corresponding in number and arrangement to saidcircumferential portions of said rotational friction surface.
 18. Thethread feed system according to claim 17, wherein two said threadguiding elements which are offset by about 90° about said rotationalaxis and assigned to said rotational friction surface are arranged on asupport which is mounted on a plunger, said plunger being connected tosaid drive means so as to be adjusted in parallel with said rotationalaxis between the adjustment positions.